"The New South Wales branch of the Labor Party has a really good history in supporting gay and lesbian causes, and there's no reason why they can't add marriage equality to that list," Mr Greenwich said.

"John Robertson obviously spoke as a member of the ALP, but he also spoke as a parent.

"I think he represented the view that many parents of gay and lesbian children have, and that is that they want their kids, their sons and daughters, to be treated equally by the law and to be protected equally by the law."

Prime Minister Julia Gillard reiterated her opposition to same sex marriage after it was legalised in New York State in the United States last week.

Mr Robertson told 7.30 he does not think the issue will have any impact on Labor's electoral chances.

"I don't think this is an issue that's going to see us lose seats or lose an election, and on the same count I don't think it's an issue that's going to see us win seats or win elections either," he said.